Mobile telephony devices utilizing wireless communication protocols are ubiquitous. Many of these devices utilize one of the competing cellular networks (e.g., GSM or CDMA) to place and receive telephone calls to other telephony endpoint devices. A telephony endpoint device may include another mobile telephony device on the same or another cellular network, a Voice-over-IP (VoIP) telephony device, and/or a plain old telephone service (POTS) telephony device. Each of these telephony endpoint devices may use a different access network but all are interfaced at some point to allow for communication among the different networks.
Recently, there has been introduced another type of mobile telephony device, one that is capable of utilizing multiple different networks depending on the current location or network conditions pertaining to the mobile telephony device. Such a mobile telephony device may be characterized as a hybrid mobile device due to its capability of making and receiving telephone calls on at least two distinct networks. Some hybrid mobile devices include the ability to start or establish a telephone call on one network (e.g., an IP based VoIP network over a WiFi connection) and handoff the call to a second network (e.g., a cellular network) when conditions on the original network degrade. Such a handoff may occur, for instance, when the mobile hybrid device moves out of range of the IP based WiFi access point. Rather than dropping the call, the hybrid mobile device, in conjunction with the a network based server, may switch to a cellular connection prior to severing the WiFi VoIP connection thereby ensuring that the hybrid mobile device stays connected to the other telephony endpoint and the call is not dropped.
Described herein are methods, systems, and techniques for implementing such an inter-network handoff for a hybrid mobile.